Railgun system

ABSTRACT

A system for accelerating an armature to launch a projectile by injecting liquid aluminum between the armature and a pair of electrically conductive rails. A system for accelerating an armature by injecting liquid metal between the armature a plurality of electrically conductive rails and collecting the liquid metal. The liquid metal or liquid aluminum can comprise solid particles. A railgun structure with mechanical guide rails. A railgun structure with a film stack of alternating copper and nickel layers. An armature with guide rail supports. A method of using the system by placing liquid metal in the armature, placing the armature between conductive rails, and applying an electric current to the rails.

RELATED PATENT APPLICATIONS

This patent application is a divisional application of U.S. patentapplication Ser. No. 12/537,482 filed Aug. 7, 2009 entitled “RailgunSystem”, and further claims the benefit of U.S. Provisional Application61/189,834 filed Aug. 23, 2008, U.S. Provisional Application 61/192,602filed Sep. 20, 2008, U.S. Provisional Application 61/205,263 filed Jan.17, 2009, and U.S. Provisional Application 61/217,340 filed May 28,2009, all five of which previously-filed patent applications are herebyincorporated by reference in their entireties into the present patentapplication.

BACKGROUND

Electromagnetic launchers, such as railguns, have received considerableinterest due to their ability to accelerate projectiles without use ofexplosives. A railgun uses the magnetic field between twocurrent-carrying rails to accelerate a current-carrying armature.Railguns are a promising non-explosive projectile launcher and have manypotential applications, including mining. For widespread use, a railgunmust be economic and powerful.

However, existing systems that can electromagnetically accelerate aprojectile suffer from one or more deficiencies, such as raildegradation and less than optimal projectile speed. It is common for atypical railgun system to be unusable after ten to fifty launches due torail degradation from heat and friction. An increase in launchesavailable from a railgun can significantly lower the cost of launches.Since high projectile speed is important for most railgun applications,improvements to optimize projectile speed also are needed.

Accordingly, there is a need for a railgun system that overcomes one ormore of these deficiencies of existing systems.

SUMMARY

The present invention is directed to a system that satisfies this need.In a method of the system, an armature is placed between electricallyconductive rails, where there is a gap between at least part of thearmature and the rails, electrical current is applied to the rails toaccelerate the armature in a forward direction, and liquid metal isintroduced into at least a portion of the gap. The liquid metal can besubstantially only liquid aluminum or an aluminum alloy, and preferablyhas a temperature between about 700° C. and about 2200° C. The liquidmetal typically is injected near the rear of the armature in the forwarddirection. Preferably at least some of the introduced liquid metal iscollected by the armature.

The liquid metal can be provided in the armature by placing the metal ina container, heating the metal to melt it, and then placing thecontainer in the armature. Alternatively, the metal is heated to meltit, and then it is placed into the container. A third technique is toheat the metal to melt it and then place the liquid metal directly intothe armature. The heating can be done with induction heating.

The liquid metal can contain solid particles. The solid particles canhave a density close to that of the liquid metal. The solid particlescan be a mixture of two materials, one denser than the other, such ascarbon and tungsten. The tungsten can be deposited onto the carbon.

An apparatus according to this system suitable for launching aprojectile comprises the armature, the electrically conductive railsthat form the gap between at least part of the rails and the armature, asource of electricity, electrically conductive liquid metal stored inthe armature that comprises at least 90% aluminum, and a port thatdirects the liquid metal into at least a portion of the gap. There is agun barrel having a discharge end with a bore containing the conductiverails. The armature has a chamber for containing the liquid metal. Thechamber can be lined with corrugated titanium.

When a container is used for the liquid metal, the container is placedin the chamber in the armature. The container preferably isnon-electrically conducting, and can be made of quartz or ceramic. Thecontainer can optionally have a piston for pressuring liquid metal fromthe chamber, a discharge opening, and foil across the discharge opening.When the armature is accelerated, the liquid metal breaks the rail andflows out through the discharge opening. The foil is thin enough thatpressure from the liquid metal breaks the foil when the armatureaccelerates. The container can also have multiple liquid metal regionsseparated by foil and heated to different temperatures.

The armature has a housing that supports a projectile. The armature canalso have a backing supported by the rear of the armature that conductsthe current between the rails. The backing can be planar. The armaturecan also have a collector that collects the introduced liquid metal.

The armature port for introducing liquid metal can have one or moreinjector slots that inject the liquid metal between 10 degrees and 90degrees relative to the forward direction. Preferably the apparatusincludes a stop that prevents the liquid metal from reaching the forwardend of the armature. The stop can be made substantially of carbon. Thebacking and housing can be made of an aluminum alloy while the port canbe made of a titanium alloy.

The conductive rails typically are formed of copper or copper alloy.Optionally the conductive rails can have a metallic deposit thereon. Themetallic deposit can be one or more layers of a nickel alloy.Alternatively, the metallic deposit can have alternating layers of acopper alloy and a nickel alloy. The layers can have a thickness fromaround 2μ to around 200μ. The rails can also have a top layer made of analuminum alloy.

Optionally there are one or more insulators attached to the conductiverails and the gun barrel. Preferably there is a sump at the dischargeend of the gun barrel for catching liquid metal.

Preferably there is at least one guide rail in the bore of the gunbarrel. The guide rail can be segmented into pieces about 5 mm long withabout 1 mm gaps between the pieces. The armature can have guide railengaging projections to keep the armature on track, and preferably tworail projections on one surface and two projections on the opposedsurface. Each projection can be provided with a replaceable bufferelement, typically formed of titanium, to avoid wear on the projectionsand guide rails.

DRAWINGS

These and other features, aspects and advantages of the presentinvention will become understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 is an exploded perspective view of a system according to thepresent invention;

FIG. 2 is a perspective view of the system of FIG. 1 where thecomponents are assembled;

FIG. 3 is an exploded perspective view of an armature for use in thesystem of FIG. 1;

FIG. 4 is a sectional view of the armature shown in FIG. 3 taken on line4-4 in

FIG. 3;

FIG. 5 is a front perspective view of the armature of FIG. 3 where thecomponents are assembled together;

FIG. 6 is a rear perspective view of the armature of FIG. 3 where thecomponents are assembled together;

FIG. 7 is a perspective exploded view of the gun bore and railcomponents of the system of FIG. 1;

FIG. 8 is a front elevation view, partly in section, of a gun bore withassociated rails of the system of FIG. 1;

FIG. 9 is a perspective view, partly in section, of the gun boreaccording to the present invention of FIG. 1;

FIG. 10 is partial longitudinal sectional view of the gun bore accordingto the present invention of FIG. 1 depicting the exit cavity; and

FIG. 11 is a schematic block diagram of a method of using one embodimentof the present invention.

DESCRIPTION

Introduction

According to one embodiment of the present invention, there is provideda system for accelerating an armature for the purpose of launching aprojectile.

As used herein, except where the context requires otherwise, the term“comprise” and variations of the term, such as “comprising,” “comprises”and “comprised” are not intended to exclude other additives, components,integers or steps. Thus, throughout this specification, unless thecontext requires otherwise, the words “comprise”, “comprising” and thelike, are to be construed in an inclusive sense as opposed to anexclusive sense, that is to say, in the sense of “including, but notlimited to”.

As depicted in the Figures, all dimensions specified in this disclosureare by way of example only and are not intended to be limiting. Further,the proportions shown in these Figures are not necessarily to scale. Aswill be understood by those with skill in the art with reference to thisdisclosure, the actual dimensions of any device or part of a devicedisclosed in this disclosure will be determined by its intended use.

The devices of the present invention and their component parts can beconstructed according to standard techniques, as will be understood bythose with skill in the art with reference to this disclosure.

Overview

Referring now to FIGS. 1 and 2, a system 100 having features of thepresent invention comprises an armature 102 for use with a railgunstructure 104. The railgun structure 104 comprises parallel electricallyconductive rails 106 and an electricity source 108 conductivelyconnected to the electrically conductive rails 106. An electric currentis applied in one direction on one electrically conductive rail 106 andin an opposite direction on another electrically conductive rail 106 andtherefore there is a magnetic field present between the electricallyconductive rails 106. The electrically conductive rails 106 can be madesubstantially of copper. In a preferred embodiment, the railgunstructure 104 further comprises at least one guide rail 110 forstability.

Armature

Referring now to FIGS. 3-6, the armature 102 is configured to support aprojectile. The armature 102 has a projectile support such as a bore202. The projectile can be used for mining. Between the armature 102 andconductive rails 106 is a gap 204. The armature 102 comprises a housing208 for supporting the projectile, a chamber 210 for receivingelectrically conductive liquid metal, and a liquid metal dispensing port212 for introducing electrically conductive liquid metal into at least aportion of the gap 204. The liquid metal is introduced generally in aforward direction as shown by 206 in FIG. 6. By “forward direction”there is meant the direction the armature 102 is accelerated.

The electrically conductive liquid metal can be at least 90% liquidaluminum. It can be an aluminum alloy, but preferably it issubstantially pure aluminum. The liquid metal serves to bridge the gap204 between the electrically conductive rails 106 and the armature 102to minimize electrical contact resistance between the armature and therails. In a preferred embodiment, the electrically conductive rails 106are first treated with a layer of solid aluminum. With liquid aluminuminjected onto the electrically conductive rails 106, there can be anamount of the liquid aluminum that adheres to the electricallyconductive rails 106 and an aluminum oxide byproduct residue that formson this surface. The solid aluminum thickness can vary along the lengthof the railgun structure 104 and can be at least 10μ thick. The liquidaluminum injected onto the electrically conductive rails 106 can meltthe underlying layer of solid aluminum, breaking up any aluminum oxidebyproduct residing on top of the solid aluminum. In a preferredembodiment, the injected liquid aluminum is substantially pure.

The liquid aluminum can contain solid particles 214 for assisting inbreaking up the aluminum oxide layer. The solid particles 214 preferablyhave substantially the same density as aluminum. This similar densityallows a substantially uniform distribution of the solid particles 214in the liquid metal. The solid particles 214 can be manufactured fromtwo materials of different density. For example, the solid particles 214can be made of carbon fibers with tungsten deposits. As carbon fibershave diameters varying from 5μ to 8μ, the tungsten layer isapproximately 0.5μ thick to ensure the particles have substantially thesame density as liquid aluminum.

The liquid metal dispensing port 212 is in liquid communication with thechamber 210 by a liquid communication conduit 216. Typically the chamber210 is configured to hold at least 1 kg, typically less than 2 kg, andpreferably about 1.4 kg of liquid metal. The housing 208 can be made ofaluminum and the chamber 210 is in the housing 208. The chamber 210 canbe lined with a material with a high melt temperature, such ascorrugated titanium, to directly receive the liquid aluminum. The liquidmetal can be heated as it enters the chamber 210, such as throughinduction heating. The liquid metal can be injected at varying rates ofspeed as it passes through the induction heater to allow the liquidmetal to have a range of temperatures. The chamber can have multiplecorrugations for insulating the liquid metal. Alternatively, the chamber210 can be configured to receive a container 218 that holds heatedliquid metal and is made of a material with a melting temperature higherthan aluminum, such as quartz or ceramic. The container 218 can receivesolid aluminum and then be heated to melt the aluminum. An inductionheater, such as a single turn inductive coil having a major axis, can beused to melt the aluminum in the container 218. Preferably, thecontainer 218 is moved through the single turn inductive coil along themajor axis from 1 to 2 times until the aluminum melts or is within 100°C. of the melting temperature, which heats the rest of the container 218and prevents cracking. The container 218 can then be moved through theinductive heater again to fully melt the aluminum. To allow a range ofliquid aluminum temperatures, the container 218 can be moved at varyingrates of speed through the induction heater, with slower speeds creatinghotter temperatures. Liquid aluminum from previous launches can formsediments of uneven thickness on the electrically conductive rails 106.These different temperatures are desirable for more efficiently breakingup the aluminum sediments on different sections of the electricallyconductive rails 106. Alternatively, the aluminum can first be heatedand then deposited in the container 218.

The melted aluminum is maintained at a temperature ranging from about700° C. to about 2200° C. While aluminum at temperatures at about 2200°C. is more efficient at transferring heat, the high temperature couldcause rail degradation. Typically the melted aluminum is maintained at atemperature ranging from about 700° C. to about 1100° C., and preferablyat about 1000° C. The melted aluminum, when introduced into at least aportion of the gap 204, preferably has a temperature less than themelting temperature of the electrically conductive rails 106.

As shown in FIG. 4, the container 218 has a front end 219 and a rear end221, wherein the front end 219 is sealed and the rear end 221 comprisesa discharge opening 220, wherein the discharge opening 220 is coveredwith a foil 222 having a melting temperature higher than the temperatureof the melted aluminum, such as tantalum foil. The container 218optionally can have a piston 224 located between the liquid aluminum andthe front end 219. The piston must have sufficient mass to inject theliquid metal from the port 212 at ballistic speeds. When the armature102 accelerates in the direction shown by the forward direction 206arrow in FIGS. 5 and 6, the piston 224 is forced towards the rear end221 of the container 218 by its own inertia. The piston's movementforces the liquid aluminum towards the rear end 221 of the container218, breaking the foil 222 and allowing the liquid aluminum to movetowards the dispensing port 212 through the liquid communication conduit216.

Instead of a single chamber for the aluminum, there can be multiplechambers, such as four chambers 210, each chamber 210 holding acontainer 218 of liquid aluminum. Optionally, each container 218 isprovided with one or more thin and semi-insulating foils for insulatingregions of liquid aluminum from each other. The thin and semi-insulatingfoils can be made substantially of tantalum. The thin andsemi-insulating foils serve to separate sections of the liquid aluminumthat have different temperatures and are configured to break as thearmature 102 accelerates. The liquid aluminum proximal to the rear end221 of the container 218 can be hotter than the liquid aluminum proximalto the front end 219 of the container 218.

The armature 102 can have a conductive backing 226 made of electricallyconductive material such as aluminum. The backing 226 can be attached tothe rear of the dispensing port 212 and can be 4 cm thick. The backing226 conducts electric current between the electrically conductive rails106. Electric current flows from one electrically conductive rail 106through the liquid metal to the backing 226 and to the otherelectrically conductive rail 106 through liquid metal. Preferably, thebacking 226 has at least two opposed, longitudinal surfaces parallel tothe electrically conductive rails 106 and one lateral surface connectingthe two longitudinal surfaces. Electric current travels from theelectrically conductive rails 106 through the liquid metal to onelongitudinal surface. The current traveling on the longitudinal surfacemoves in a direction 180 degrees from the forward direction 206. Thecurrent moving in this direction helps to maintain the gap 204 betweenthe electrically conductive rails 106 and the armature 102 through theLorentz force. The current then travels along the lateral surface in adirection 90 degrees from the forward direction 206. The current thentravels along the other longitudinal surface in the forward direction206. The current moving in this direction also helps to maintain the gap204. In a preferred embodiment, the backing 226 is substantially planar.The planar design serves to maximize Lorentz force in the forwarddirection 206 and not toward the electrically conductive rails 106,thereby optimizing the speed of the armature when it is accelerated.

The dispensing port 212 delivers the liquid metal into at least aportion of the gap 204, causing a circuit bridge between theelectrically conductive rails 106 and the armature 102. In a preferredembodiment, the dispensing port 212 comprises a delivery channel 228 inliquid communication with the liquid communication conduit 216, amanifold area 230 in liquid communication with the delivery channel 228,and an injector slot 232 in liquid communication with the manifold area230 and the gap 204. Liquid aluminum flows from the chamber 210 via thedelivery channel 228 to the injector slot 232 through the manifold area230. The injector slot 232 can have a plurality of struts 233. Thestruts 233 can be machined using standard electrical discharge machining(EDM) techniques. The struts 233 are angled to direct the liquid metalat an angle relative to the forward direction 206 toward the nearestelectrically conductive rail 106. The angle can be from 10° to 90°, andpreferably is 30°. The struts 233 have ends 234 near the gap 204, andthe ends 234 form a line referred to as the “injector length” having twoends. The struts 233 can each have a second angle relative to theforward direction 206 toward the center of the injector length. Thesecond angle can vary by strut 233 and can be proportional to thedistance of the strut 233 to the center of the injector length. Thesecond angle can be as high as 50° relative to the forward direction 206toward the center of the injector length for struts at the ends of theinjector length. The injector length can be curved to allow a largervolume of liquid metal into the gap 204 than if the injector length werestraight. In a preferred embodiment, the struts 233 have a heightbetween 25μ and 125μ, near the gap 204, such as 100μ. Preferably, thestruts 233 also have a thickness from about 0.1 mm to about 1 mm and arespaced from about 2 mm to about 10 mm apart.

The dispensing port 212 optionally can include a heat conduction region236 for breaking up solid aluminum sediments on the electricallyconductive rails 106. The heat conduction region 236 allows for atemporary deposit of liquid metal to ensure a relatively constant amountof liquid metal in contact with the electrically conductive rails 106and the armature 102. The heat conduction region 236 is located in frontof the injector slot 232 proximal to the strut ends 234 and can be adepression from about 1μ deep to about 150μ deep.

In a preferred embodiment as shown in FIGS. 3 and 4, the armature 102has a stop 238, which can be made of carbon, such as graphite, toprevent injected liquid metal from traveling forward to the housing 208.Carbon is preferable as it creates micron level contact with theelectrically conductive rails 106. The stop 238 can be flush with theelectrically conductive rails 106 to block the liquid metal. Typically,the stop 238 is embedded in the housing 208 and installed at an anglefrom about 95° to about 135° relative to the forward direction 206. Thestop 238 can have a width from about 1 cm to about 5 cm and a thicknessfrom about 1 cm to about 5 cm. As the armature 102 accelerates, the stop238 wears down due to friction with the electrically conductive rails106. The thickness from about 1 cm to about 5 cm means the stop 238 doesnot completely disintegrate in one launch. The stop 238 preferably hasone or more arms oriented 180° relative to the forward direction. Thearms preferably extend to the injector length to prevent liquid metalfrom traveling above or below the armature 102.

Preferably, the armature 102 has a collector 240 for collecting spentliquid metal. The spent liquid metal resides in the collector 240 andexits the system 100 with the armature 102. The collector 240 and thedispensing port 212 can be a unitary unit, made of a material with ahigher melt temperature than aluminum, such as titanium or a titaniumalloy. In a preferred embodiment, the collector 240 is located in frontof the injector slot 232 and just behind the stop 238. Liquid metalflows from the heat conduction region 236, and the stop 238 forces theliquid metal to the collector 240 as there is nowhere else for theliquid metal to go. In a preferred embodiment, the distance between theinjector slot 232 and the collector 240 is at least 2 cm. In anotherpreferred embodiment, the volume of the collector 240 is greater thanthe volume of the liquid metal so that all of the dispensed liquid metalcan be collected.

The armature 102 can have one or more guide rail engaging projections242 designed to fit into a corresponding guide rail 110 to help maintainthe armature traveling in the forward direction 206. In a preferredembodiment, the armature 102 further comprises at least one replaceablebuffer 244 attached to each projection 242 and located proximal to theguide rail 110 to prevent wear of the guide rails 110 and theprojections 242. The buffer 244 can be made of a titanium alloy and canbe from about 2 mm thick to about 4 mm thick.

Railgun Structure

The railgun structure 104 can especially be seen in FIGS. 7-9. Theelectricity source 108 provides electric current in one direction alongone rail 106 and in another direction along the other rail 106. Theelectrically conductive rails 106 can be 16 cm wide and 3 cm thick. Theparallel electrically conductive rails 106 form a plane, and theelectric current from the electricity source 108 causes a magnetic fieldbetween the two rails pointed into the plane between the electricallyconductive rails 106.

Preferably the electrically conductive rails 106 have a metallic depositto prevent deformation or erosion from the hot liquid aluminum. Themetallic deposit can be made from a single layer of a deposit metal from2μ to 200μ thick, and preferably is 100μ thick. Alternatively themetallic deposit can be a plurality of layers, wherein the layersalternate between a deposit metal and copper. The deposit metalpreferably has a thermal expansion coefficient similar to that of themetal used for the electrically conductive rails 106, a melt temperatureabove the melt temperature of the metal used for the electricallyconductive rails 106, a thermal diffusion coefficient lower than that ofthe metal used for the electrically conductive rails 106, a surfacehardness greater than that of copper, and an atomic diffusion intoaluminum lower than the metal used for the electrically conductive rails106 into aluminum. The deposit metal can be nickel or nickel alloy. Eachlayer has a thickness between about 2μ and 200μ and the outermost layeris nickel or nickel alloy. Preferably the outermost layer is 100μ thick.The number of alternating layers in the stack can range from one pair toabout five pairs. The metallic deposit can be attached to theelectrically conductive rails 106 using standard electroplatingtechnology as developed for the electronics industry.

In a preferred embodiment, the electrically conductive rails 106, withor without the deposit materials, are coated with solid aluminum duringmanufacture to ensure the copper-aluminum interface is an oxide-freeinter-metallic bond. The aluminum is the outermost layer of theelectrically conductive rails 106. This can be done with standardmetallurgical techniques, such as electroplating followed by a heatcycle.

In a preferred embodiment, the railgun structure 104 comprises a gunbarrel 302 having an inner surface 304, and at least one insulator 306attached to the inner surface 304 of the gun barrel 302 and to theelectrically conductive rails 106. The gun barrel 302 can be about 12 cmthick, 12 m long, and can be made from a non-conducting material. Thegun barrel 302 can have an inner diameter of about 60 cm. Thenon-conducting material can be a glass fiber winding with anelectrically insulating adhesive to bind the glass together, such aspolyaryletheretherketone (PEEK) or epoxy. The glass fiber windings canbe preloaded. The insulator 306 can be made of a dielectric material,such as ceramic, silicon carbide, or glass fiber held together with PEEKor epoxy. Alternatively, the gun barrel 302 can be preloaded with aninflatable bladder according to Jackson et al. in U.S. Pat. No.7,503,248. The electrically conductive rails 106 have an accelerationsurface direction pointed away from the insulator 306.

With reference to FIG. 9, the railgun structure 104 preferably furthercomprises at least one guide rail 110 attached to the gun barrel 302.The guide rail 110 is configured to fit with the rail support 242 on thearmature 102 and can be attached to an insulator 306, wherein theinsulator 306 is attached to the inner surface 304 of the gun barrel302. The insulator 306 can be made of a dielectric material, such asceramic, silicon carbide, and glass fiber held together with PEEK orepoxy. The guide rail 110 can comprise a plurality of segments about 5mm long and spaced apart from each other from about 0.5 mm to about 1mm. The guide rail 110 can be made of hardened steel or tungsten alloyand can be from about 1 cm thick to about 2 cm thick. Preferably theelectrically conductive rails 106 in the gun barrel 302 are at about 0°and 180°, with a first guide rail 110 at about 90°, and a second guiderail 110 at about 270°. Optionally, the railgun structure 104 canfurther have a third guide rail 110 proximate to the first guide rail110 and a fourth guide rail 110 proximate to the second guide rail 110,with the armature 102 having four guide rail engaging projections 242,each corresponding to a respective guide rail 110.

The railgun structure 104 can include an exit cavity 310 attached to thefront of the gun barrel 302 as shown in FIG. 10 for preventing a flashwhen a projectile exits the gun barrel 302. The exit cavity 310 isconfigured to contain any remaining amount of injected liquid metal. Theelectrically conductive rails 106, insulators 306, and guide rails 110protrude out of the gun barrel 302 and into at least a portion of theexit cavity 310. The exit cavity 310 comprises an insulating barrel 312,a removable attachment 314 designed to connect to the insulating barrel312, a cover 316 attached to the front of the insulating barrel 312 witha hole 318 in the middle of the cover 316 at least the size of thearmature 102, and a sump 320 attached to the removable attachment 314.Preferably, the guide rails 110 and the insulators 306 attached to theguide rails 110 extend up to the cover 316 to guide the armature throughthe length of the exit cavity 310. The insulating barrel 312 is fromabout 100 to about 200 cm long and about 12 cm thick. The attachment 314is from about 50 to about 100 cm tall, from about 20 cm to about 40 cmlong, about 10 cm thick, and is at least as wide as the armature 102 istall. Preferably, at least part of the attachment 314 is angled towardsthe hole 318 in order to angle the sump 320, allowing the sump 320 tocatch more incident liquid metal. The attachment 314 is designed to beremovable to facilitate replacing the sump 320 without disassembling theentire exit cavity 310. The attachment 314 and insulating barrel 312 canbe made of an insulator, such as wound glass fiber held together withPEEK or epoxy. The electrically conductive rails 106 can be angledtowards the insulating barrel 312 to taper off the electric current andpreferably extend to at least the back of the sump 320 so liquid metalis incident only on the sump 320. When there is insufficient electriccurrent going through the armature 102, the magnetic field between theelectrically conductive rails 106, and thus the acceleration of thearmature 102, terminates. Some liquid metal may continue to exit thearmature 102 due to residue pressure on the liquid metal in the chamber210, albeit much less than while accelerating. In addition, there may besome remaining liquid metal in the gap 204 and the heat conductionregion 236. This liquid metal is incident on the sump 320.

The sump 320 can be made from the same metal as the incident liquidmetal. The sump 320 can have a length and width substantially the sameas the length and width of the attachment 314, and a thickness fromabout 30 cm to about 50 cm. Preferably, the sump 320 and the liquidmetal are at least 90% aluminum. The sump 320 can comprise a pluralityof pockets 322 with one or more divisions 324 between the pockets 322,similar to a honeycomb. The pockets 322 can be angled to catch incidentliquid metal. The pockets 322 can have openings 326 from about 0.5 cm²to about 4 cm². Preferably, the divisions 324 have a thickness nogreater than 0.5 mm proximate to the openings 326 so the incident liquidmetal does not splash off the divisions 324. The sump 320 can beroughened by a procedure such as abrasive cleaning. The abrasivecleaning process can comprise bead blasting, then removing the beadblast material using a distilled water ultrasonic wash, and thenremoving aluminum oxide or other contaminants using a standard wetchemical etch. The roughness allows deposited liquid metal to better fitin the pockets 322 and prevents flaking, thereby increasing the numberof launches before replacing the sump 320.

The exit cavity 310 can be filled with a substantially non-reactive gas,such as nitrogen, which helps avoid aluminum oxidation. The exit cavity310 can further comprise nitrogen injectors that fill the exit cavity310 with nitrogen when the armature 102 is accelerated out of the system100 to prevent an inrush of atmospheric gases.

Method

To use the system 100, with reference to FIG. 11, a user first deliversliquid metal into the armature 102 through one of a variety oftechniques. In a first technique 402, a user first places metal in thecontainer 218, melts the metal inside the container 218, and then placesthe container 218 in the chamber 210. In a second technique 404, a userreverses the placing and the melting steps. In a third technique 406, auser melts the metal and then places the metal directly into the chamber210. Once the liquid metal is in the armature, the user then places thearmature 102 between the electrically conductive rails 106. The user canforcefully inject the armature so as to prevent the armatureself-welding to the electrically conductive rails. One way to do this iswith an impulse injection such as an air hammer. Alternative, a user canplace the armature 102 between the electrically conductive rails 106 sothat initially no conductive portion of the armature and the conductiverails are in contact and then place the liquid metal inside the armature102 using one of the three techniques described above. The user thenapplies an electric current to the electrically conductive rails 106 andbrings a portion of the conductive armature in direct contact with aportion of the conductive rail to accelerate the armature 102. Themomentum of the armature 102 causes the liquid metal to be injected intoat least a portion of the gap 204. Preferably, the liquid metal is thencollected by the armature 102 and stored therein to prevent damage tothe system 100.

Applications

The previously described embodiments of the present invention have manyapplications, including accelerating a projectile for mining and fornon-explosive projectile launching in a weapons system. The embodimentscan also be used to launch raw materials to supply a space station ormoon colony, as well as to launch unmanned gliders.

Advantages

The previously described embodiments of the present invention have manyadvantages, including a larger railgun range due to the reduced contactresistance between the armature and the electrically conductive railsthrough the liquid metal. In addition, this reduced contact resistanceis maintained over the entire rail length from gun breach to muzzle.There is less rail degradation due to the presence of nickel andaluminum on the electrically conductive rails and the liquid metalcontact, as well as the lack of a Lorentz force induced sliding contactpressure between the armature and conducting rail. The latter is animprovement over state-of-the-art solid armature railguns that rely onexcessive sliding contact pressure for reducing inter-electrode contactresistance. Further, the exit cavity attenuates the existing muzzleflash from launching a projectile from a railgun. This reduced muzzleflash allows for greater concealment from objects such as low-orbitsatellites and environmental and personnel hazards in the vicinity ofthe railgun.

Although the present invention has been described in considerable detailwith reference to the preferred versions thereof, other versions arepossible. Therefore the scope of the appended claims should not belimited to the description of the preferred versions contained therein.

1. An apparatus suitable for launching a projectile comprising: a. anarmature for accelerating the projectile; b. electrically conductiverails for accelerating the armature, there being a gap between at leasta portion of the armature and the rails; c. a source of electricity forapplying electric current to the rails to accelerate the armature; d.liquid metal in the armature, the liquid metal comprising at least 90%aluminum; and e. a port for directing the liquid metal into at least aportion of the gap.
 2. The apparatus of claim 1 wherein the armaturecomprises a chamber substantially lined with corrugated titanium forcontaining the liquid metal.
 3. The invention of claim 1 wherein theliquid metal contains solid particles.
 4. The invention of claim 3wherein the solid particles have substantially the same density as theliquid metal.
 5. The invention of claim 3 wherein the solid particlescomprise first and second materials, one denser than the other.
 6. Theinvention of claim 5 wherein the first material is carbon and the secondmaterial is tungsten.
 7. The invention of claim 6 wherein the tungstenis deposited onto the carbon.
 8. The apparatus of claim 3 wherein thearmature comprises a chamber holding at least one container of liquidmetal.
 9. The apparatus of claim 8 wherein the container isnon-electrically conducting.
 10. The apparatus of claim 9 wherein thecontainer is formed of a material selected from the group consisting ofceramic material and quartz material.
 11. The apparatus of claim 8wherein the container farther comprises: a. a piston; b. a dischargeopening in liquid communication with the port; and c. foil across thedischarge opening, the foil being sufficiently thin that the pressure ofliquid metal breaks the foil when the armature is accelerated.
 12. Theapparatus of claim 11 wherein the container further comprises aplurality of liquid metal regions heated to different temperatures.